Medical treatment using vascular catheters is developing to smaller and smaller blood vessels as from the heart to the brain. Lesions of the brain blood vessels are aneurysm, arteriovenous malformation (AVM) and dural arteriovenous fistula (DAVF), for example. Demand for a vascular catheter for treating or examining such lesions of blood vessels is more and more increasing.
A vascular catheter for this purpose must be inserted to the intended part of a blood vessel being passed in complicatedly bent or branched blood vessels.
For an intravascular surgical operation called emboluation technique conducted for treating lesions in the brain blood vessels such as aneurysm and arteriovenous malformation, for example, the distal end of a small-diameter vascular catheter is inserted to or near the lesions in the brain. Then, a liquid embolizing material such as cyanoacrylate or dimethylsulfoxide solution of ethylene-vinyl alcohol copolymer, a granular embolizing material such as granules of poly(vinyl alcohol) or a expanding member such as coil is injected from the distal end of the catheter.
For such a small-diameter vascular catheter, high manipulability to insert it easily and quickly up to a target lesion passing in complicatedly bent or branched small blood vessel is required in addition to the chemical and biological safety required for common vascular catheters.
To have high manipulability, a small-diameter vascular catheter must have the following four properties.
The first property is that the catheter can convey the pushing force in the direction of the axis added to the proximal end portion by the operator up to the distal end or has so called pushability.
The second property is that the catheter can convey the turning force around the axis added to the proximal end portion up to the distal end or has so called turnability.
The third property is that the catheter can be advanced in blood vessels along the guide wire inserted beforehand easily and without causing damage to the wall of the blood vessels or has so called pliability.
The fourth property is that the catheter does not kink at bents (curves and crooks) in blood vessels after the guide wire is removed or has reluctance to kinking.
A vascular catheter having a catheter body of the double-tube structure made up of a comparatively rigid inner tube and a comparatively soft and flexible outer tube covering the outside surface of the inner tube and having the distal end portion extending beyond the distal end of the inner tube and forming the tip of the catheter body was developed and currently used.
In more detail, U.S. Pat. No. 4,385,635 discloses a vascular catheter in which the inner tube is formed of polyamide and the outer tube is formed of polyurethane and the distal end portion is tapered so that the inner diameter becomes gradually smaller to the distal end. This catheter has a problem that it kinks easily at the boundary between the two-tube portion and the single tube portion because of the abrupt change of the rigidity at the boundary.
Japanese utility model application published under Publication No. 17082/1987 discloses a vascular catheter which uses the outer tube formed of silicone rubber and the inner tube formed of a hard synthetic resin selected from among polyethylene, polypropylene, fluororesin and hard vinyl chloride. In this catheter, a step of the height equal to the wall thickness of the inner tube is formed in the lumen at the boundary between the two-tube portion and the single tube portion. Because of the step, this catheter kinks easily at the boundary and hence has small reluctance to kinking.
Further, a vascular catheter recently put to practical use which uses the inner tube formed of polypropylene and the outer tube formed of ethylene-vinyl acetate copolymer has also the same problem of small reluctance to kinking.